The driving methods for an Organic Light Emitting Display (OLED) pixel circuit may be divided into a current-driven method and a voltage-driven method. FIG. 1 shows a voltage-driven pixel circuit, and FIG. 2 shows a current-driven pixel circuit. In the voltage-driven pixel circuit, the formula for the output current IOLED is as follows:
            I      OLED        =                  1        2            ⁢                        μ          n                ·        Cox        ·                  W          L                ·                              (                          Vdata              -              Voled              -              Vth                        )                    2                      ,
where μn is a carrier mobility, Cox is a gate oxide capacitance, W/L is a width-to-length ratio of a transistor, Vdata is a data voltage, Voled is an OLED light emitting operation voltage shared by all pixel units, and Vth is a threshold voltage of the transistor. For an enhancement-type Thin Film Transistor (TFT), Vth is a positive value. For a depletion-type TFT, Vth is a negative value. It can be known that if Vth of a pixel varies with time, the output current IOLED of the pixel at different times will be different. The afterimage phenomenon will occur, and a stable display of an Organic Light Emitting Diode (OLED) display temporally cannot be ensured. The advantage of the current-driven method with respect to the voltage-driven method is that the output current IOLED is always equal to the input current Idata. In the current-driven pixel circuit, even if the threshold voltage Vth of the pixel varies with time, the current-driven pixel circuit can adjust autonomously to ensure that the output current IOLED is always equal to the input current Idata, so as to realize a uniform display spatially and a stable display temporally of the OLED. This is because that the operation process of the current-driven pixel circuit may generally be divided into two stages, the first of which is a pre-charging stage, and the second of which is a light emitting stage. At the pre-charging stage, the output current IOLED is equal to the input current Idata, at the same time, charge is stored in a capacitor of the current-driven pixel circuit. At the light emitting stage, since the charge has been stored in the capacitor of the current-driven pixel circuit, it can be ensured that the output current IOLED in the current-driven pixel circuit is still equal to the output current IOLED at the pre-charging stage, i.e., still equal to the input current Idata at the pre-charging stage. A particular current-driven pixel circuit is as shown in FIG. 3, in the circuit, there is an input terminal of an external control voltage Vctrl for supplying the voltage to the circuit in the light emitting stage, which is connected to a gate of a TFT, and an input terminal of an operation voltage VDD of the circuit is connected to one of a source and a drain of the TFT. A simulated signal waveform chart of the circuit is as shown in FIG. 4. An inverse signal synchronized with the signal input from the input terminal of a pre-charging control voltage Vselect for supplying the voltage to the circuit in the pre-charging stage is input from the input terminal of the external control voltage Vctrl, to realize a supply of voltage to the driving circuit by the pre-charging control voltage Vselect in the pre-charging stage, and a supply of voltage to the circuit by a voltage combined by the external control voltage Vctrl and the operation voltage VDD through a TFT connected thereto, ensuring the output current IOLED of the current-driven pixel circuit existing in the light emitting stage. However, the existence of the external Vctrl input terminal will decrease the aperture ratio of the pixels. With the decrease of the aperture ratio of the pixels, the lifetime of the OLED is decreased.